This invention relates to an improved circuit breaker and more particularly to a circuit breaker in which the magnetic trip assembly includes an armature having a nib extending angularly therefrom, the nib having a detent which is engaged by biasing means.
Circuit breakers provide protection for electrical systems from electrical fault conditions such as current overloads and short circuits. Typically, circuit breakers include a spring powered operating mechanism which opens electrical contacts to interrupt the current through the conductors on an electrical system in response to abnormal currents. The operating mechanism is unlatched by a trip bar which in turn is operated by a trip mechanism associated with each phase of the electrical system. The trip mechanism can include a magnetic trip device comprising a fixed magnetic structure energized by the current flowing through the conductor, and a movable armature which is attracted toward the stationary magnetic structure to operate the trip bar. The trip bar in turn unlatches the operating mechanism to open the electrical contacts in each phase of the electrical system. The movable armature is biased away from the stationary magnetic structure by a spring, called a torsion spring, thereby forming a gap between the armature and the stationary magnetic structure in the absence of an abnormal current.
Several different types of adjustment means have been suggested for adjusting the level of current which the magnetic trip device actuates the operating mechanism. One such adjustment is to vary the spring bias applied to the armature by the torsion spring. However, the torsion spring is placed in the circuit breaker, and the circuit breaker is enclosed by the molded case. Thus, it is difficult to adjust the torsion spring or replace it once the case is molded. Also, if it is desired to place more force on the torsion spring, a spring back force is caused which can adversely effect the performance of the breaker. Finally, because the torsion spring is in the molded case and can not be adjusted, the torsion spring is not available to compensate for manufacturing and assembly variations in the other parts of the circuit breaker.
What is needed, therefore, is a circuit breaker that includes a magnetic trip assembly in which the biasing force applied to the movable armature is consistently and accurately controlled and can be calibrated and adjusted.